Multiple string for a ball game racket

ABSTRACT

The present disclosure relates to a string for a ball game racket including at least two parallel filaments, wherein only portions of the filaments are interconnected. Moreover, the disclosure relates to method of producing such a string. A first method includes the steps of providing at least two string filaments, bringing the string filaments together into a parallel configuration and combining portions of the string filaments. An alternative production method includes the steps of providing a string and slitting portions of the string so as to produce at least two parallel filaments of the string, only portions of which are interconnected.

The present invention relates to a multiple string for a ball game racket, in particular a tennis, squash, badminton, racquet ball or paddle tennis racket, having sections of varying structure. Moreover, the present invention relates to a method of producing such a multiple string.

Conventional strings for such rackets are typically made of different natural materials or plastics materials and may consist of several layers, such as a core and a jacket. DE 200 16 733 U1, e.g. discloses a racket string comprising a toothed core made of a first plastics material having a toothed outer surface and a jacket layer made of a second plastics material and moulded onto the core such that it is joined with its toothed outer surface. The first plastics material has a hardness and an abrasion resistance that are lower than those of the second plastics material.

Moreover, racket strings with a core-sheath structure are known from DE 38 75 704 T4. According to one embodiment, the string has a conjugate monofilament structure with one or more core parts surrounded by one or more sheath layers. According to a further embodiment, the string according to DE 38 75 704 T4 has a winding-strands structure, i.e. a string consisting of a core and winding strands wound around the core, said core and said strands being adhesively secured to each other, both the core and the winding strands being composed of a monofilament of synthetic resin, and the core and the winding strands having different diameters. In this embodiment, either the core or the winding strands is/are made of the conjugate monofilament. According to a further embodiment, the string has a twisting-strands structure, i.e. the string consists of plural synthetic resin monofilament strands that are twisted together and adhesively secured to one another by an adhesive.

Moreover, strands are known in the art whose cross-section has a non-circular shape, as disclosed, e.g., in DE 27 37 751 A1 and DE 18 31 958. DE 851 450 C and DE 85 01 864 U1 disclose strings having a wound structure of a plurality of individual elements.

In all these known types of string designs, the shape, structure and composition along the string are essentially constant.

It is an object of the present invention to provide a string for a ball game racket with improved properties, in particular an improved force transmission from racket to ball as well as better handling. This object is achieved by the features of the claims.

The present invention is based on the idea that for tuning a ball game racket a combination of different properties in one string and an optimum adaptation to the respective requirements are important. To this end, the string according to the present invention has portions of different structure in the longitudinal direction. Thus, the properties of the strings of a ball game racket can be essentially improved.

According to the invention, the string is a multiple string comprising at least two preferably essentially parallel filaments, portions of which are connected to each other. Each joining portion in which the filaments are interconnected is followed by a portion in which the filaments are unconnected, i.e. in which the loose filaments run parallel.

The longitudinal proportion of the joining portions with respect to entire length of the string is preferably between 10% and 80%, more preferably between 25% and 60% and particularly preferably between 35% and 50%. The length of one joining portion is preferably 20 mm to 200 mm, more preferably 50 mm to 150 mm and particularly preferably 80 mm to 120 mm. The length of the portions in which the two filaments are unconnected, is preferably 50 mm to 250 mm, more preferably 100 mm to 200 mm and particularly preferably 130 mm to 170 mm.

In an embodiment of the present invention, the individual filaments consist of conventional racket strings. In a further embodiment of the present invention, the filaments consist of parts of conventional strings of sports rackets. A multiple string according to the present invention may comprise two or more filaments of the same or a different type. According to the invention, it is preferred to combine a plurality of filaments that differ in cross-section, dimensions (e.g., diameter), material and/or quality. In particular, the filaments may be conventional multi-filament and/or single-filament strings. The diameter of the respective filaments is variable, however, preferably in a range between 0.5 mm and 1 mm, particularly preferably in a range between 0.65 mm and 0.8 mm.

Moreover, the present invention relates to a method of producing such a multiple string. A substantially conventionally produced racket string serving as a filament for the string according to the present invention is provided with a coating that allows portions of the filaments to be joined later. The two or more filaments thus coated run parallel (i.e., in substantially the same longitudinal direction) and longitudinally pass a mechanism that allows portions of two or more filaments to be permanently connected. This mechanism preferably uses high temperatures, ultraviolet light or laser light to join the filaments by means of the coating. This mechanism may be used selectively, i.e. in restricted areas, such that a connection is merely established in the joining portions.

In a further method of producing a multiple string according to the present invention, the portions in which the filaments are not interconnected are produced on the basis of a conventional racket string by longitudinally slitting portions of the string.

In the following, preferred embodiments of the string according to the present invention are exemplarily described on the basis of the drawings, in which:

FIG. 1 shows a schematic side view with an enlarged section of an embodiment of the string according to the present invention illustrating portions of unconnected and portions of connected filaments;

FIG. 2 shows a schematic side view of a another embodiment of the multiple string according to the present invention;

FIGS. 3 a-3 f show schematic cross-sectional profiles of both unconnected and connected portions of different embodiments of multiple strings according to the present invention;

FIG. 4 shows a schematic view of the method of producing a multiple string according to the present invention; and

FIG. 5 shows a diagram illustrating the coefficient of restitution of a racket if strung with a conventional string and if strung with a string according to the present invention.

FIG. 1 shows an embodiment of a string 1 according to the present invention and an enlarged section thereof. There are a first filament 3 and a second filament 5 as well as joining portions 7 in which the two filaments 3, 5 are interconnected. Between two adjacent joining portions 7, there is in each case a portion 9 in which the two filaments 3, 5 are unconnected. In this embodiment of the multiple string, the joining portions 7 are designed such that the material 11 joining the two filaments 3, 5 is not only between them but envelopes the two filaments 3, 5.

FIG. 2 shows a further preferred embodiment of a string 1 according to the present invention in the form of a double string. This double string 1 is also provided with two filaments 3, 5, joining portions 7 in which the two filaments 3, 5 are interconnected and a portion 9 in-between in which the two filaments 3, 5 are unconnected. In this embodiment of double string 1, the two filaments 3, 5 are connected such that the joining material 11 is substantially only between these two filaments.

FIG. 3 shows different cross-sectional profiles of a plurality of embodiments of the multiple strings according to the present invention, in each case in an unconnected portion 9 (FIGS. 3 a, 3 c and 3 e) and in a joining portion 7 (FIGS. 3 b, 3 d and 3 f). FIG. 3 a shows the cross-sectional profile of a double string 1 according to the present invention, in a portion 9 in which the two filaments are unconnected. In this embodiment of double string 1, the two filaments 3, 5 have substantially equal cross-sections and equal diameters. FIG. 3 b shows the cross-sectional profile of the same double string 1, however, in joining portion 7, in which the two filaments 3, 5 are interconnected.

FIG. 3 c again shows a cross-sectional profile of a further embodiment of a double string 1; however, here, the first filament 3 has a larger diameter than the second filament 5. FIG. 3 d shows double string 1 according to FIG. 3 c in a joining portion 7, in which the two filaments 3, 5 are interconnected.

FIG. 3 e shows the cross-sectional profile of a further embodiment of string 1 according to the present invention, here in form of a triple string, wherein again a portion 9 is shown in which the three filaments are unconnected. In this embodiment, the first and second filaments 3, 5 have the same diameter, while a third filament 13 has a smaller diameter. FIG. 3 f shows triple string 1 according to FIG. 3 e in a joining portion 7, in which the three filaments 3, 5, 13 are interconnected.

As evident from FIGS. 3 a, 3 c and 3 e, the individual filaments 3, 5, 13 run substantially parallel in the unconnected portions 9 without being interconnected or coupled. The filaments may also be spirally or helically wound around each other. The cross-sections according to FIGS. 3 b, 3 d and 3 f show that the individual filaments 3, 5, 13 are permanently coupled in the joining portions 7 or integrally joined.

The longitudinal proportion of the joining portions 7 with respect to the entire length of string 1 is preferably between 10% and 80%, more preferably between 25% and 60% and particularly preferably between 35% and 50%. The length of a joining portion 7 is preferably 20 mm to 200 mm, more preferably 50 mm to 150 mm and particularly preferably 80 mm to 120 mm. The length of portions 9, in which filaments 3, 5, 13 run unconnected, is preferably 50 mm to 250 mm, more preferably 100 mm to 200 mm and particularly preferably 130 mm to 170 mm.

FIG. 4 schematically shows a production method of producing an embodiment of string 1 according to the present invention in the form of a double string. In this figure, production is from right to left. Starting on the right, there are two filaments 3, 5 that are coated by a respective coating means 15, 17 assigned to these filaments. Alternatively, coating with a common coating means is also possible.

Upon coating, the individual filaments 3, 5 are brought together via a guiding mechanism 19, e.g., in the form of pulleys. Guiding mechanism 19 is capable of bringing the—depending on the string configuration—two or more filaments 3, 5 together so that they run, e.g., parallel. Moreover, filaments 3, 5 may be twisted together, interlaced or arranged in another way by guiding mechanism 19 such that they run parallel.

Subsequently, the two now parallel filaments 3, 5 pass a joining mechanism 21 in which portions of the filaments 3, 5, which were coated before, are permanently joined. This joining mechanism 21 preferably uses high temperatures, ultraviolet light or laser light to interconnect filaments 3, 5 by means of their coating. Mechanism 21 can be used so selectively, i.e. in such restricted areas, that a connection is only established within joining portions 7.

Eventually, finished double string 1 may be wound in a roll.

FIG. 5 shows the result of a measurement for determining the coefficient of restitution of a ball game racket. A ball is shot with a predetermined speed at the fixed racket, whereupon the velocity of the rebounded ball is measured. This measurement was taken at different spots of the racket, comprising in one case a conventional string and in the other case a string according to the present invention. The dashed line shows the coefficient of restitution of the racket at different positions of the racked head for a string according to the present invention, whereas the continuous line shows the same measurement for a conventional racket string. As evident, the string according to the present invention guarantees a considerably improved coefficient of restitution, resulting in higher rebounding forces.

In portions 7, in which the filaments 3, 5, 13 are interconnected, the multiple strings according to the invention have the properties and the appearance of a conventional racket string, whereas in portions 9, in which the filaments 3, 5, 13 are unconnected, the properties and the appearance of the multiple string resembles the properties and the appearance of a bundle of two or more individual strings running parallel. Thus, the properties of the multiple string according to the present invention are defined by a combination of properties of the individual portions. Consequently, the properties of the multiple string may be varied, e.g., by varying the proportion of the lengths of the portions with connected and unconnected filaments. However, it is, for example, also possible to provide a ball game racket with a multiple string according to the present invention such that in predetermined areas of the racket head there are only string portions in which the filaments are interconnected and in other areas of the racket head there are only string portions in which the filaments are unconnected. Thus, areas of the racket head having different desired properties may be selectively provided. In a tennis racket comprising an embodiment of the multiple string, for example, the transmission of forces onto the ball in the centre of the stringing is considerably better than in a racket comprising conventional strings. 

1. A string for a ball game racket, comprising at least two parallel filaments, wherein only portions of the filaments are interconnected.
 2. The string according to claim 1 wherein the filaments are of the same type.
 3. The string according to claim 1, wherein the filaments have different diameters and/or qualities.
 4. The string according to claim 1, wherein the interconnected portions of the filaments and unconnected portions of the filaments follow each other, wherein a longitudinal proportion of the interconnected portions of the filaments with respect to an entire length of the string is between 10% and 80%.
 5. The string according to claim 1, wherein the interconnected portions of the filaments are permanently interconnected in a longitudinal direction via their outer surfaces.
 6. The string according to claim 1, wherein the interconnected portions of the filaments have a length between 20 mm and 200 mm.
 7. The string according to claim 1, wherein unconnected portions of the filaments have a length between 50 mm and 250 mm.
 8. The string according to claim 1, wherein the filaments have a diameter of 0.5 mm to 1 mm.
 9. A method of producing a string for a ball game racket, comprising the steps of: a) providing at least two string filaments; b) bringing the string filaments together to form a parallel configuration; and c) connecting portions of the string filaments.
 10. The method according to claim 9, wherein before being brought together the string filaments are coated.
 11. The method according to claim 9, wherein the portions of the string filaments are connected using elevated temperature, ultraviolet light, and/or laser light.
 12. A method of producing a string for a ball game racket, comprising the steps of: a) providing a string; and b) slitting portions of the string so as to produce at least two parallel filaments of the string, only portions of which are interconnected.
 13. The string according to claim 1, wherein a longitudinal proportion of the interconnected portions of the filaments with respect to an entire length of the string is between 25% and 60%.
 14. The string according to claim 1, wherein a longitudinal proportion of the interconnected portions of the filaments with respect to an entire length of the string is between 35% and 50%.
 15. The string according to claim 2, wherein the interconnected portions of the filaments are permanently interconnected in a longitudinal direction via their outer surfaces.
 16. The string according to claim 3, wherein the interconnected portions of the filaments are permanently interconnected in a longitudinal direction via their outer surfaces.
 17. The string according to claim 1, wherein the interconnected portions of the filaments have a length between 80 mm and 120 mm.
 18. The string according to claim 1, wherein unconnected portions of the filaments have a length between 130 mm and 170 mm.
 19. The string according to claim 1, wherein the filaments have a diameter of 0.65 mm to 0.8 mm.
 20. The method according to claim 10, wherein the portions of the string filaments are connected using elevated temperature, ultraviolet light, and/or laser light. 